Therapeutic agents and imaging contrast agents sometimes suffer drawbacks stemming from high clearance and/or high toxicity. For example, even though some studies have shown that β-cyclodextrin (β-CD) and its derivatives, including hydroxypropylβ-cyclodextrin (HP-β-CD), may be useful in the treatment of the typically fatal disease Niemann-Pick type C (NPC), high dosages of the administered β-CDs or derivatives thereof are required since their persistence in the bloodstream is brief (>90% is cleared within 24 hours). With regard to imaging contrast agents, a majority of clinically used contrast agents, though they may have high paramagnetism, excellent relaxation enhancement, and stability, they suffer from rapid clearance from the body, such that they are ineffective, e.g., for angiographic enhancement. In some instances, nanoparticulate platforms used as carriers of, e.g., Gd3+, though they have better pharmacokinetics than other clinically used contrast agents, suffer from issues such as acute toxicity and poor water accessibility. There is therefore a need in the art for therapeutic agents for treating, e.g., NPC, and imaging contrast agents that do not suffer from the drawbacks enumerated herein.